The present invention relates to the filtration arts. It finds particular application in conjunction with the filtering of suspended matter from waste water, either as an independent system or in conjunction with a separate biofiltration system which removes dissolved organic and inorganic materials from the water. It is to be appreciated, however, that the invention is also applicable to other water treatment processes where removal of suspended material or dissolved organic and inorganic matter is desirable, such as the treatment of water for use in fish tanks or chemical processes or for treatment of bodies of water such as ponds, streams and small lakes and waste water from industrial or mining operations.
Treatment of waste waters has become increasingly important in view of stricter environmental regulations concerning industrial and municipal wastes. Because of regulations concerning contaminant disposal, it is desirable to degrade contaminants in the waste water prior to disposal. Treatment of water for reuse has also increased, as a means of providing purified water for industrial, domestic and aquaculture systems, such as fish farms. Biological filtration systems, incorporating a filtration medium for physically trapping particulate matter, together with microorganisms for degrading certain contaminants, are widely used in water treatment.
Commonly used biofiltration systems employ a packing material which becomes coated with microorganisms immobilized in a biofilm layer. One such system is described in U.S. Pat. No. 5,494,574 to Unterman et al. The coated packing material simultaneously traps suspended particles, while the microorganisms act on the biodegradable components of the waste water.
Filtration systems suffer from downtime problems due to clogging of the packing material with solid material from the waste water. A number of methods have been developed for removing this trapped material. In one method, the packing material is subjected to turbulent flow, created by mechanical mixers, such as propellers, as shown in U.S. Pat. Nos. 5,445,740 and 5,126,042, to Malone. Alternatively, a circulating system continuously circulates the packing material through the chamber, as shown in U.S. Pat. No. 5,494,574 to Unterman et al.; U.S. Pat. No. 5,573,671 to Klein; and U.S. Pat. No. 5,429,740 to Van Der Herberg. In yet another system, intermittent air scouring of the entire bed is used to remove the trapped material, as described in U.S. Pat. No. 5,487,829 to Safferman et al. and U.S. Pat. No. 5,232,586 to Malone.
Such methods for cleaning of the filter suffer from a number of drawbacks. Mechanical methods, such as propeller agitation, tend to damage the biofilm. Air scouring methods are less destructive of the film, but less effective at cleaning the filtration media.
Accordingly, it has been considered desirable to develop a new and improved water filtration system that does not require extensive down time for cleaning the filter and employs a cleaning process which leaves biofilms deposited on the filtration particles intact. The present invention provides a new and improved apparatus and method for filtration of dissolved and suspended matter from water which overcomes the above referenced problems and others.